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Cloning and Stem Cells: Definitions of Key Terms | Valerie Schmalz | July 16, 2005

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Cloning or somatic cell nuclear transfer.
An unfertilized egg has its nucleus removed or inactivated, and replaced with the nucleus from a donor cell. This donor cell nucleus, containing the DNA, is stimulated to interact with the egg, and a new embryo develops that is genetically identical to the being providing the body cell. (Source: U.S. Conference of Catholic Bishops.)

Embryonic stem cells:
Primitive (undifferentiated) cells derived from the inner cell mass of the embryo with the potential to become a wide variety of specialized cell types. Embryonic stem cells can be drawn from embryos created in any manner: those created via in-vitro fertilization and cloning are the most common sources. (Based on National Institutes of Health definition. Source: President’s Council on Bioethics.)

Adult stem cell:
An undifferentiated cell found in a differentiated tissue that can renew itself and (with certain limitations) differentiate to yield all the specialized cell types of the tissue from which it originated. (Source, President’s Council on Bioethics, www.bioethics.gov). Can be found throughout the body, including in umbilical cord blood where it has been found to be able to differentiate beyond to create more diverse cells to treat diseases such as leukemia and aplastic anemia.

Totipotent cell:
has the capacity to turn into an entire organism. A cell that can give rise to the entire organism, including the extra-embryonic membranes; the fertilized egg or zygote is totipotent. (Source: President’s Council on Bioethics.)

Pluripotent cell:
A cell that can produce all the cell types of the developing body; embryonic stem cells, as well as the inner cell mass cells of the blastocyst, are pluripotent. (Source: President’s Council on Bioethics.)

Pluripotent stem cell:
Any stem cell that has the same functional capacity–that is, stable pluripotency–as an embryonic stem cell, though not necessarily the same origin. (Source: President’s Council on Bioethics.)

Stem cells
: Stem cells are undifferentiated multipotent precursor cells that are capable both of perpetuating themselves as stem cells and of undergoing differentiation into one or more specialized types of cells. (Source: President’s Council on Bioethics.)

In-Vitro Fertilization:
The union of an egg and sperm, where the event takes place outside the body and in an artificial environment (the literal meaning of "in vitro" is "in glass"; for example, in a test tube). (Source: President’s Council on Bioethics.)

IVF embryo:
An embryo produced by in vitro fertilization. (Source: President’s Council on Bioethics.)

Altered Nuclear Transfer (ANT):
A proposed method, using a modified form of somatic cell nuclear transfer (SCNT), of producing a biological artifact from which human pluripotent stem cells could be derived. Proposed to the President’s Council on Bioethics in December by Dr. William Hurlbut. (Source: President’s Council on Bioethics.)

Oocyte Assisted Reprogramming (OAR):
The theory of oocyte-assisted reprogramming would involve transferring the nucleus of an adult cell — the nucleus is the part of the cell that contains the genetic code — into an egg without its own nucleus, to create a new cell. Because of prior genetic alterations to both the transferred nucleus and the egg, the resulting cell — the OAR theory proposes — would in fact be a pluripotent stem cell with properties identical to embryonic stem cells. Where it differs from cloning is that the goal of OAR is to use the egg lacking its own nucleus to directly transform the transferred nucleus into a pluripotent stem cell completely skipping any embryonic stages. (Source: Fr. Nicanor Austriaco.) Entire explanation available here.

Unfertilized egg cell. (Source: President’s Council on Bioethics.)

Other helpful definitions:

Biological artifact:
As employed in the ANT theory, this phrase denotes an artificially created non-embryonic but embryo-like cellular system, engineered to lack the essential elements of embryogenesis but still capable of some cell division and growth. (Source: President’s Council on Bioethics.)

Process of removing tissue from patients for diagnostic examination. (Source: President’s Council on Bioethics.)

Blastomere biopsy:
Removal of one or two blastomeres from the embryo in vitro at about the 8-cell stage, usually in order to perform preimplantation genetic diagnosis and screening. (Source: President’s Council on Bioethics. )

In experimental embryology, the individual produced by grafting an embryonic part of one animal on to the embryo of another, either of the same or of another species. (Source: President’s Council on Bioethics. )

Cord blood:
Blood in the umbilical cord and placenta. (Source: President’s Council on Bioethics. )

A procedure whereby differentiated, somatic cells are restored to a more undifferentiated, multipotent condition. (Source: President’s Council on Bioethics. )

(a) In humans, the developing organism from the time of fertilization until the end of the eighth week of gestation, when it becomes known as a fetus. (NIH) (b) The developing organism from the time of fertilization until significant differentiation has occurred, when the organism becomes known as a fetus. An organism in the early stages of development. (Source: President’s Council on Bioethics. )

A functional unit of heredity that is a segment of DNA located in a specific site on a chromosome. A gene directs the formation of an enzyme or other protein. (NIH) (Source: President’s Council on Bioethics. )

Other Online Resources:


Also see the following IgnatiusInsight.com articles:

FEATURE: Does Pro-Life Cloning Exist? The Debate Rages On | Valerie Schmalz | June 16, 2005
Cloning and Stem Cell Bills Set To Be Up For Senate Debate | Valerie Schmalz | July 16, 2005

Valerie Schmalz is a writer for IgnatiusInsight. She worked as a reporter and editor for The Associated Press, and in print and broadcast media for ten years. She holds a BA in Government from University of San Francisco and a Master of Science from the School of Foreign Service at Georgetown University. She is the former director of Birthright of San Francisco. Valerie and her wonderful husband have four children.

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